1. Field of the Invention
This invention relates to a light emitting semiconductor device, and more particularly to a light emitting semiconductor device of the type which incorporates a sub-mount for mounting to a mount such as a leadframe. The present invention also relates to a method of making such a semiconductor device.
2. Description of the Related Art
In recent years, various light emitting semiconductor devices have been developed. In particular, a blue light emitting diode (blue LED) with a high brightness has been made available, wherein gallium nitride (GaN) compound crystal layers are successively grown on a sapphire substrate by organic metal chemical vapor deposition (hereafter abbreviated as "MOCVD").
Specifically, as shown in FIG. 11 of the accompanying drawings, a GaN type blue LED comprises a sapphire substrate 70 on which a GaN buffer layer 71 is formed, and a crystal layer laminate is formed on the buffer layer 71. The laminate includes two N-type semiconductor layers 72 (GaN and AlGaN layers represented as a single layer in FIG. 11), a light emitting semiconductor layer 73 (InGaN layer), and two P-type semiconductor layers 75 (AlGaN and GaN layers also represented as a single layer in FIG. 11). A cathode electrode 75 is formed on the N-type GaN layer, whereas an anode electrode 76 is formed on the P-type GaN layer, as also shown in FIG. 12.
The LED described above is mounted on a mount. A typical example of the mount is a leadframe 77 having a first lead 77a (anode lead) and a second lead 77b (cathode lead).
In assembly, the sapphire substrate 70 is bonded on the first lead 77a of the leadframe 77 by an adhesive for example. Further, the cathode electrode 75 is electrically connected to the second lead 77b of the leadframe 77 through a bondwire 78, whereas the anode electrode 76 is electrically connected to the first lead 77a through another bondwire 79.
In operation, a drive voltage is applied across the first and second leads 77a, 77b. As a result, the LED is activated for light emission from the side of the P-type layers 72 in a direction perpendicular thereto.
According to the arrangement described above, wirebonding need be performed at least at two positions. This causes an increase of time and labor required for mounting the LED relative to the leadframe 77, thereby leading to a cost increase.
Further, since the LED is made to emit light from the side of the P-type layers 72, the anode electrode 76 provided on the side of the P-type layers occupies a part of the light emitting area A indicated in FIG. 12. This means that the part of the light emitting area A occupied by the anode electrode 76 is not utilizable for light emission. Thus, even if the LED is designed to have a capability of generating light with a high brightness, it is impossible to provide a sufficient amount of light, thereby failing to meet the demand for high luminosity indication in addition to posing limitations on the location and configuration of the anode electrode 76. Such a problem becomes even more serious if the area assumed by the anode electrode 76 becomes larger.